Synergistic wall construction method

ABSTRACT

A thermal barrier and air barrier system is described.

PRIORITY CLAIM

This application claims priority from U.S. Application No. 62/554,553, filed Sep. 5, 2017, which is incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to a wall construction system and method for construction of residential and commercial structures.

BACKGROUND

Due to global warming concerns, commercial and residential curtainwall construction has become building code regulated. The purpose is to reduce the amount of energy required to heat and maintain the desired temperatures. These codes include the IECC (International Energy Conservation Code). There are other codes that are very similar in scope and are widely used by architects to design buildings and the materials used. These codes, as they relate to curtain wall construction, have 2 major requirements is that must be met. The first is the thermal aspect. This requirement involves making the wall thermally resistant by requiring the wall to possess a required R or U value depending on the geographical location of the wall per International Code Council Section C401-2015 The second requirement is the requirement of a durable air barrier system that controls the amount of outside air penetration and warm interior air escaping through the building walls. Since the total energy saving equation is about both reducing the rate that cold air can enter a wall, but also the ability of the wall to hold the warm air in and the cold air out (or vice versa) in the case of high winds per International Code Council (ICC) C402.5-2015. Regarding the thermal requirements, the code council as provided a “prescriptive method” to deal with the thermal issue. In the case of Light Gage Steel Construction, it involves enveloping the total outside steel construction with various thicknesses of Poly foam on the exterior surface of the wall to achieve the desired thermal effect. It also includes Insulation Batts As the requirements have grown on the curtail walls, the foam thicknesses have grown to the point that construction has become significantly more difficult and expensive. As a side issue, the code has never dealt with steel fasteners that penetrate the thermal barrier. In the case of a brick veneer facade, the brick requires metal anchors that must connect to the steel structure located behind the thick foam. These metal anchors transmit hot and cold through the foam and into the building interior, therefore short circuiting the thermal resistant wall. There are various methods to resolve this but all of them are additional expense, complicated and additional labor.

With the addition of an air barrier to the code with the intent to reduce air infiltration, additional materials have been added on top of the already expensive and cumbersome thermal barrier. With all these things considered, the curtainwall costs have skyrocketed and steel curtainwall construction is becoming prohibitive.

SUMMARY

In one aspect, current methods to achieve both code requirements have been handled by individual companies that want to see the use of their current products grow and are not considering what is most cost effective for solving both issues effectively as shown, for example, in FIGS. 1-4.

In general, a wall system can include a thermally resistant steel stud and spray foam insulation on a side of the steel stud.

In certain embodiments, the wall system can include a plurality of thermally resistant steel studs arranged in a wall format and a foam board on the side of the side of the steel stud.

In certain embodiments, the wall system can include an air barrier adjacent to the foam board.

In certain embodiments, the wall system can include a batt insulation between the steel studs.

In another aspect, a method of building a thermally resistant wall can include installing a plurality of thermally resistant steel studs to form a cavity and spraying foam insulation to fill the cavity with foam insulation that passes through voids of the thermally so resistant steel studs.

In another aspect, a wall can include a thermally resistant steel stud, spray foam insulation, and an air barrier on an outer surface of the wall.

Other embodiments are within the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic drawing of an embodiment of a wall system.

FIG. 2 is a schematic drawing of another embodiment of a wall system.

FIG. 3 is a schematic drawing of another embodiment of a wall system.

FIG. 4 is a schematic drawing of another embodiment of a wall system.

FIG. 5 is a close up of a schematic drawing of an embodiment of a wall system.

FIG. 6 is a schematic drawing depicting a thermalinear gradient.

FIG. 7 is a schematic drawing depicting a thermal stud.

FIG. 8 is a schematic drawing depicting a standard stud.

DETAILED DESCRIPTION

The wall system described herein can include a wall system can include a thermally resistant steel stud and spray foam insulation on a side of the steel stud. Details are provided as follows.

Wall Sweating

The current state of the art design for steel stud wall, as recommended by the IECC, involves a Continuous Insulation wrap on the exterior of the building. This CI wrap is a polyiso foam material that envelopes the entire exterior surface of the building. This recommendation was driven by the fact that prior to this recommendation, it was not uncommon to find interior walls in the colder climates with condensation stripes on the interior wall surfaces. The condensation would collect directly in front of the steel studs. The standard steel studs are such poor insulators of cold temperatures, the walls surface temperatures were below the dew point of the interior air, resulting in the condensation (aka ‘Sweat’) collecting on the walls. The CI wrap protects the stud from ever seeing low temperatures thus preventing the transfer those temperatures to the inside wall surfaces. In addition to the sweating on the interior wall surfaces, there were documented cases of condensation collection on the fiber glass insulation resulting in mold and mildew collecting on the interior wall cavity over time.

Method

The method of construction proposed here is a system approach to the total requirements. The result is a construction method that will meet both code requirements by creating a synergistic design of a thermal resistant stud and a spray foam insulation encapsulated between an exterior and interior sheet. The synergy of these 2 elements meet both code requirements for both thermal and air barrier. This synergistic approach to meeting the code requirements also solve several other construction issues that include: In addition, the total thickness of the wall can be significantly reduced and conserve desirable real-estate.

The method proposed here is a thermally resistant steel stud in combination with sprayed polyisocyanurate (or equivalent product). The result is a construction method that will meet both code requirements by creating a unique synergistic design of a thermal resistant stud and a spray foam insulation.

This method described in this patent involves constructing the curtain wall with an internal wallboard (drywall), thermally insulated studs and a weather resistant exterior sheet wallboard (per code). Once constructed, a spray foam insulation material is sprayed inside the wall cavity onto the backside of the exterior sheet. Spray wet polyiso onto all seams between the exterior sheets and the joints where the exterior sheet meets the thermal stud. (FIG. 5) All paths where air can enter the wall cavity from the outside are to be filled with polyiso. In some cases, the excessively large gaps and holes will need to be covered with tape or other product prior to spraying the polyiso.

For the purposes here, the foam could be sprayed onto the back side of the interior sheet provided the interior sheet also meets the code. Although it is most practical in most installations to spray the foam onto the back side of the exterior sheet, it will work as effectively with the foam insulation sprayed on the back of the interior sheet. The code allows the air barrier to either the inside or outside of the wall.

The spray foam creates a) an air barrier sufficient to meet IECC Air Barrier Requirements, b) insulating characteristics required to meet the IECC Thermal Requirements and together with the thermal resistant stud, eliminate the need to have the expensive and cumbersome Continuous Insulation (CI) as per the prescriptive method.

It should be noted that the IECC code allows for alternative design concepts to meet the IECC codes. The methods prescribed here will meet those requirements.

Key Synergy Results

A key component of the synergy between the thermal resistant stud and the spray foam is that the thermal resistant stud keeps the stud temperature above the dew point as it approaches the interior wall. The stud creates a high thermal linear gradient that keeps the cold temperatures above the dew point as it becomes exposed to the moist warm interior air. (FIG. 6). As the thermal linear gradient transitions between the cold outside air and the warm inside air, the temperature rises above the dew point before it emerges from the air tight spray foam and is exposed to the warm moist interior air. One of the attributes of the spray foam includes the ability to keep the moist air from contacting the steel surface it is covering. The standard steel stud has a very low thermal linear gradient and results in moisture collecting inside the wall cavity. This factor is reason this method of construction will not work with the standard steel stud. The moisture collected inside the wall can produce multiple problems inside the wall which include mold and mildew.

In cases of extreme cold and heavy gage steel, the spray foam can be sprayed more heavily on the stud web area to protect the stud from exposure to condensation moist warm air when testing shows necessary.

Resulting Improvements

There are multiple practical and financial advantages to the synergy of the thermal resistant stud and spray foam insulation. These include: 1) significant reduction of labor by requiring one group of labor to apply the spray the foam into the interior cavity. The prescriptive method requires at least 3 groups of labor for insulation batting, exterior foam and air barrier. It may even require a 4^(th) group by spraying a insulated foam to cover brick attachment hardware. The labor used to spray insulation from the inside of the building does not require scaffolding construction. At least 3 of the 4 groups with the prescriptive method will require scaffolding to apply. 2) The overall wall thickness is reduced by at as much as 20% since the insulation material that is now on the exterior of the structure is moved inside of the structural members. 3) As the thermal requirements increase, the thickness of the foam on the exterior increases. That added thickness of foam makes the ability to attach the exterior façade more difficult both from the installers finding the steel studs they want to attach and the mechanics of cantilevered siding so far away from the steel structure holding it up.

All methods shown in this patent application applies with any stud that is designed to reduce the thermal conductivity between the exterior and interior wall surfaces. In some design situations, It may require other materials in addition to the thermal stud and sprayed polyiso. Those conditions would also be covered in this patent. It is reasonable to assume that hidden pockets that cannot be reached with the spray polyiso would require alternative measures to properly seal and insulate the wall. It also reasonable to have an architect require tape or other coating in addition to the thermal Stud and sprayed polyiso. These conditions are also covered by this patent.

The thermally resistant steel stud maintains the structural requirement of the wall and the resulting thermal resistance increases the temperature of the stud above the dew point before it is exposed to the warm moist interior wall cavity.

Moving the insulation from the exterior of the wall to the interior of the wall cavity results in easier and less expensive attachments of brick ties and any exterior fascia materials to the structural steel studs as required by the architects.

Thermal Resistant Stud

For purposes in this paper, a thermally resistant steel stud is any steel stud that has higher thermal resistance across the web area between the two sheeting mounting surfaces than the current mainstream design. The mainstream design is primarily a solid web with periodic holes or slots in the web area to allow wiring to pass through and stabilizing metal clips and channel. Thermal insulating studs include steel studs with oversize holes in the web area.

What makes a thermal resistant stud resistant to transfer of heat energy is the configuration of the web area that connects the outer sheeting mounting surface to the inner wallboard (drywall) surface. The rate of heat transfer is in BTU's/Hour is calculated as follows:

q=kAdT/s

where

q=heat transfer (W, J/s, Btu/hr)

A=heat transfer area (m², ft²)

k=thermal conductivity of material (W/m K or W/m ° C., Btu/(hr ° F. fr²/ft)) steel=43

dT=temperature gradient—difference—in the material (K or ° C., ° F.)

s=material thickness (m, f)

As an example: a comparison of a steel stud that is 0.045″ thick and 6 inches between the inner and outer sheet mounting surfaces:

The calculations are as follows:

Standard Stud Thermal Stud (FIG. 8) (FIG. 7) q = k A dT/s (43 × .380 × 50)/ (43 × .090 × 50)/ 6 = 136.2 7.5 = 25.8 (A) Transfer Area in an 8.45 × .045 = .380 .5 × .045 × 4 = .09 8.45″ tall Stud Cross- sectional area of the studs k = Coefficient of Thermal 43 43 Conductivity for Steel S = material thickness or 6 7.5 length of the conductive path dT = Temperature difference 50 50 between wallboard mounting surfaces (Deg f.)

The assumptions for this example include: a) studs are produced from carbon steel. This basic principle will work for other materials as well. Stainless steel has a conductivity of 11 which may become economically feasible in the future. Other materials may also become economically feasible.

Further description of a product that could be considered at thermal resistant stud would be any structural product that has been modified in a manner that effects the thermal transfer characteristics of the stud at equivalent structural strength. These characteristic changes include:

-   -   a) Alternative materials that may reduce the ‘k’ value     -   b) Reduced transfer area ‘A’ and or increased ‘S’ values of the         web area between sheet mounting surfaces.     -   c) Any changes that affect the formula shown above to produce an         overall lower value

Lab Testing

Lab testing was performed on a thermal resistant stud per ASTM C 1363-05. This test is used to determine the R-Value of different wall system designs. This test is based on an 8 ft×8 ft wall system assembly that includes exterior and interior wallboard mounted to studs and insulation filled cavity. The exterior wallboard is subjected to 50 Deg. F Air temperatures. The interior wallboard is subjected to and 100 Deg. F Air temperatures. This condition is held at these temperatures until all temperatures on the wall system stabilize. The amount of energy required to maintain this temperature is calculated and the resulting R-Value is reported. Special thermocouples were installed on the mounting surfaces of a thermal resistant stud. The side subjected to a constant 50 degrees showed a stud surface temperature 50.89 Deg. The side subject to 100 degrees showed an average 96.85 Deg. Temperature. A non-thermal resistant stud would have shown temperatures on the 100-degree side to be much lower and more in the line of 50 to 60 Deg. range. The thermal resistant stud transitioned well and ended much closer to the desired interior air temperature. The thermal linear gradient on this stud showed to be very high which is a characteristic of a thermal resistant stud. This characteristic will protect the interior walls from temperatures that will be below the dew point temperature and eliminating ‘sweat’ on the interior wall surfaces and wall cavity.

In summary, the synergistic effect of the thermally resistant steel stud and spray in foam insulation creates a unique combination of elements to satisfy both the thermal and air barrier code requirements while overcoming the physical defects that have prevented prior use of this method of construction. These attributes are summarized as follows:

Current State of the Art (Prescriptive Method) Synergy Method Requirements Meets and exceeds IECC C401 Yes Yes Thermal Code Meets and exceeds IECC C402.5 Air Yes Yes Barrier Prohibits Water Condensation in Wall Yes Yes Cavity Additional Attributes Total Labor Costs High Significantly Less Total Material Costs High Significantly Less Overall Wall Thickness for 6″ deep 8.75″ 7.25″ stud Construction Technical Difficulty High Low

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the concepts described above. Accordingly, other embodiments are within the scope of the claims. 

What is claimed is:
 1. A wall system comprising: a thermally resistant steel stud; and spray foam insulation on a side of the steel stud.
 2. The wall system of claim 1, wherein the system includes a plurality of thermally resistant steel studs arranged in a wall format and a foam board on the side of the side of the steel stud.
 3. The wall system of claim 2, further comprising an air barrier adjacent to the foam board.
 4. The wall system of claim 3, further comprising a batt insulation between the steel studs.
 5. A method of building a thermally resistant wall comprising: installing a plurality of thermally resistant steel studs to form a cavity; and spraying foam insulation to fill the cavity with foam insulation that passes through voids of the thermally resistant steel studs.
 6. A wall comprising a thermally resistant steel stud, spray foam insulation, and an air barrier on an outer surface of the wall. 